Monthly Archives: May 2006

“Nearly 100 years after his death, a monument has been unveiled to commemorate Alfred Russel Wallace, co-discoverer of natural selection – the process that drives the evolution of life on Earth. Although he is not a household name, Alfred Russel Wallace was one of the most famous scientists in the world when he died in 1913 aged 90…

The idea of natural selection as the mechanism of evolutionary change occurred suddenly to Wallace while he was suffering from a fever on the remote Indonesian island of Halmahera in February 1858. Wallace wrote down his thoughts and sent them to fellow naturalist Charles Darwin whom he knew was interested in this topic… As the well-known story goes, Lyell and Hooker decided to present Wallace’s essay (without first asking his permission), along with some unpublished fragments from Darwin’s writings on the subject, to a meeting of the Linnaean Society on 1 July 1858. [Read the full text of the Darwin-Wallace Paper here]…

During Wallace’s lifetime the theory of natural selection was widely known as the ‘Darwin-Wallace theory’ but after his death his name slipped into relative obscurity for a variety of complex reasons. The Alfred Russel Wallace Memorial Fund is trying hard to make more people (scientists included!) aware, not only of Wallace’s role as the co-discoverer of natural selection, but also of his many other important and enduring contributions to biology and wide variety of other disciplines.”

Conidiophores of Gliocladium sp. — one of the fungi to infest human corpses

A new study has described in detail, for the first time, species of fungi obtained from human corpses.

In the future, forensics experts may use the information during criminal investigations to determine when someone died – particularly in cases where the body is in an environment where little or no insect infestation has occurred.

I became interested in forensic biology thanks to the wonderful (and sorely missed) Dr Zak Erzinclioglu, who livened up the zoology department tearoom with his tales of maggots and murder. Good to read that fungi can contribute important post-mortem information too.

Spotted this site on Happibun’s page. “An intriguing applet that plots the tags in a website as a hierarchical graph.” Here’s my SU page… pretty but rather a shambles. I particularly like the yellow burst – dangling there like a Christmas bauble…

The inheritance of white feet and white tails in mice appears to be mediated by RNA.

During most of the 20th century, the laws of inheritance discovered by Gregor Mendel ruled genetics. But over the past decade, researchers have spotted numerous violations of Mendel’s laws. These exceptions, called epigenetic effects, are currently under intense study by biologists, who are searching for their underlying mechanisms. A new study suggests that at least one of the perpetrators of these anti-Mendelian acts is none other than RNA – a chemical ‘cousin’ of DNA.

A team led by developmental geneticist Minoo Rassoulzadegan of the University of Nice-Sophia Antipolis in France, made the discovery while working with mice that carry a mutant version of the Kit gene, which plays a role in coat color. Mice that are homozygous for the mutant gene – that is, animals with two copies – die shortly after birth. But heterozygotes, with one mutant and one normal Kit gene, do fine, although their feet and the tips of their tails are white rather than grey. Heterozygotes can be mated to produce offspring with two normal copies of Kit, but to the researchers’ surprise, most of these progeny also had white patches, even though the mutant gene was no longer present.

The effect appears to be due to RNA. The hypothesis is that RNA is carried in the mouse’s sperm, and at fertilisation it “silences” the activity of the normal Kit gene. This happens not only in the offspring but in subsequent generations too.

If validated, the way is open for a rethink on how RNA could influence the transmision of hereditary diseases, metabolism and even types of “imprinted” behaviour from distant generations.

“More than 50 million years ago the ancestors of whales and dolphins were four-footed land animals, not unlike large dogs. They became the sleek swimmers we recognize today during the next 15 million years, losing their hind limbs in a dramatic example of evolutionary change.

Fossil evidence shows that whales lived on land – sharing a common ancestor with hippos, deer and camels. Their transition to an aquatic lifestyle occurred long before they eliminated their hind limbs. During the transition, their limbs became smaller, but they kept the same number and arrangement of hind limb bones as their terrestrial ancestors.

The actual loss of the hind limb occurred much further along in the evolutionary process, when a drastic change occurred to inactivate a gene, Sonic hedgehog, essential for limb development.

Researchers say the findings tend to support traditional evolutionary theory, a la Charles Darwin, that says minor changes over vast expanses of time add up to big changes. And while Sonic hedgehog’s role in the evolution of hind limbs in ancient whales is becoming apparent, it is still not fully defined.”

“Confused by logarithms? If so, you’ll be surprised to hear they come naturally to pigeons and possibly, subconsciously, to you.” [really?]

There are asymmetries in the way animals perceive numbers and time, and a recent experiment involving pigeons tapping levers in response to light flashes of differing lengths, showed that these birds underestimate the midpoint between two time intervals. This fits with a logarithmic model where pigeons might perceive time on a logarithmic scale on which higher values are increasingly compressed together.

Reminds me a bit of when my children were toddlers and counted “one, two, lots!”.

“It’s been a little over a year and a half now since scientists announced the discovery of the most controversial fossil in the field of human origins: Homo floresiensis aka the Hobbit. Scientists found bones of a diminutive hominid on the Indonesian island of Flores, and estimated that it lived there as recently as 12,000 years ago. It stood about as high as a normal three year old human child and had a brain the size of a chimpanzee’s. But its bones were also found with stone tools. The scientists declared the bones were not human. Instead, they belonged to a species of their own — one that branched off from much older hominids. Later, the scientists offered brain scans and more bones to bolster their case.”

This collection of essays by Carl Zimmer chronicles the ‘hobbit wars’ between rival palaeoanthropologists — is Homo floresiensis a new species or a human pygmy, perhaps with birth defects?

“Mice are known to have a keen sense of smell, but it’s not just their noses that are adept at picking up a scent, a new study shows… Scientists at Indiana University Bloomington report biochemical machinery that allows mouse sperm cells to follow the weakest of scents. Even when ovary extracts were diluted 100,000 times, some sperm cells still found their mark.”

Understanding why, how and when sperm are attracted to ovaries may help scientists understand problems with human conception.

“Defects in sperm chemotaxis may be a cause of infertility, and consequently, sperm chemotaxis could potentially be used as a diagnostic tool to determine sperm quality or as a therapeutic procedure in male infertility.” – Stephen C. Jacobson, Indiana University Bloomington.

I was going to make a flippant remark about the excellent egg-sniffing abilities of the sperm of teenage boys… but I decided against it.

“The earliest known ancestors of modern humans might have reproduced with early chimpanzees to create a hybrid species, a new genetic analysis suggests.”

Not had a chance to give this a good read yet, so will comment later…

The timeline of human evolution is long and controversial, with significant gaps. Experts do not agree on many of the start and end points of various species – so this chart involves significant estimates.